This invention relates to transporting vehicles upon a roll back frame that is movable relative to a main frame. More particularly, the present invention relates to a mechanism for positioning the roll back frame such that it defines a relatively small approach angle with respect to the ground.
Prior art vehicle trailers are known having a roll back frame attached to a main frame. The roll back frame is moved with respect to the main frame from a transport position to a vehicle loading position at which it is pivoted with respect to the main frame and is in contact with the ground. A vehicle is moved upon the roll back frame and the roll back frame is moved back to the transport position on the vehicle. These prior art trailers have enjoyed success in recent years, however, some problems still exist with these assemblies.
One problem is that the main frame is a minimum distance above the ground to provide clearance while the trailer is being moved. The roll back frame is pivoted with respect to the main frame relative to a pivot point on the main frame. Thus, pivot point is at the same minimum distance above the ground as the main frame. This defines the approach angle the roll back frame makes relative to the ground. The greater the approach angle, the more difficult it is to move a vehicle upon the roll back frame.
These devices are often utilized for disabled vehicles that need repair and cannot be driven upon the roll back frame. Thus, it is known in the prior art to provide a mechanism for lowering the main frame and the pivot point to lessen the approach angle. One type of prior art device uses a complicated mechanism for compressing the support spring which interconnects a wheel axle to the main frame. By using this technique, the pivot point between the main frame and the roll back frame is also lowered and the approach angle is lessened. This prior art device requires manual actuation to engage and disengage the mechanism that lowers, or "squats" the pivot point. In addition, it requires several hydraulic cylinders and complex controls.
It is an object of the present invention to disclose a mechanism for "squatting" the main frame that is self-actuating as the hydraulic circuit drives the roll back frame from a transport position to a loading position.
It is further an object of the present invention to disclose such a mechanism that is self-releasing as the roll back frame moves from the loading position back to the transport position.